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5.6 MUD BRICK (Adobe)

151

material use

Mud Brick (Adobe)
The ideal building material would be
‘borrowed’ from the environment and
replaced after use. There would be little or
no processing of the raw material and all the
energy inputs would be directly, or indirectly,
from the sun. This ideal material would also
be cheap. Mud bricks can come close to
this ideal.
Basic mud bricks are made by mixing earth
with water, placing the mixture into moulds and
drying the bricks in the open air. Straw or other
fibres that are strong in tension are often added
to the bricks to help reduce cracking. Mud
bricks are joined with a mud mortar and can be
used to build walls, vaults and domes.

The use of earth construction is wellestablished in energy efficient housing. There
are many aspects to earth construction and
despite the fact that most of the world’s
buildings are made of earth and it is one of the
oldest known building materials, there is much
about its properties and potential that remains
undeveloped and poorly researched.

PERFORMANCE SUMMARY
Appearance
The appearance of mud bricks reflects the
material they are made from. They are thus
earthy, with colour determined by colour of
clays and sands in the mix. Finished walls
can express the brick patterns very strongly
at one extreme or be made into a smoothly
continuous surface.

Thermal mass
Adobe walls can provide moderate to high
thermal mass, but for most Australian climatic
conditions, as a rule of thumb, walls should be
a minimum of 300mm thick to provide effective
thermal mass. [See: 4.9 Thermal Mass]

Insulation
Paul Downton

At its simplest, mud brick making involves
placing mud in moulds which, after initial drying,
are removed to allow the bricks to dry slowly
(not in direct sun). Moulds can be made from
timber or metal – anything that can be shaped
to provide the desired size for the bricks.
Virtually all the energy input for mud brick
construction is human labour (indirectly, fueled
by the sun) and after a lifetime of use, the bricks
break back down into the earth they came
from. The most effective use of mud bricks in
building healthy, environmentally responsible
housing, comes from understanding their merits
and accepting their limitations. Mud brick
construction is often referred to as ‘adobe’
which is an Arabic and Berber word brought
by Spaniards to the Americas, where it was
adopted into English.

Structural capability
With thick enough walls, mud brick can create
load bearing structures up to several stories
high. Vaults and domes enable adobe to be
used for many situations other than vertical
walls. The mud brick may be used as infill in a
timber frame building or for load-bearing walls,
although its compressive strength is relatively
low. Typically, Australian adobe structures are
single or double storey. In the Yemen there are
buildings 8 stories high and more that have
stood for centuries! [See: 5.5 Construction
Systems]

Contrary to popular belief mud bricks are not
good insulators. Since they are extremely
dense they lack the ability to trap air within their
structure, the attribute of bulk insulation that
allows it to resist the transfer of heat. Insulation
can be added to adobe walls with linings but is
not intrinsic to the material, and, depending on
the building design may not be needed in some
climate zones. [See: 4.7 Insulation]

Sound insulation
A well-built adobe wall has very good sound
insulation properties. In fact, it can be almost
equivalent to a monolithic masonry structure
in its capacity for sound attenuation. [See: 2.7
Noise Control]

Fire and vermin resistance
Since earth does not burn, and earth walls do
not readily provide habitat for vermin, mud brick
walls generally have excellent fire and vermin
resistance.

material use

152

Durability and moisture resistance
Adobe walls are capable of providing structural
support for centuries but they need protection
from extreme weather (eg. with deep eaves) or
continuous maintenance (the ancient structures
of the Yemen have been repaired continuously
for the centuries they have been standing).
As a general rule, adobe needs protection from
driving rain (although some adobe soils are
very resistant to weathering) and should not be
exposed to continuous high moisture.

Breathability and toxicity
Mud bricks make ‘breathable’ walls but some
mud brick recipes include bitumen, which
potentially results in some outgassing of
hydrocarbons. Ideally earth should be used
in its natural state or as near it as can be
achieved.

Environmental impacts
Mud bricks have the potential to provide the
lowest impact of all construction materials.
Adobe should not contain any organic matter
– the bricks should be made from clays and
sands and not include living soil. They require
very little generated energy to manufacture, but
large amounts of water. The embodied energy
content of mud bricks is potentially the lowest
of all building materials but additives, excessive
transport and other mechanical energy use can
increase the ‘delivered’ embodied energy of all
earth construction. [See: 5.2 Embodied Energy]

5.6 MUD BRICK (Adobe)

good networks in Australia including a broad
based national organisation, the Earth Building
Association of Australia (EBAA), which is a
not for profit organisation “formed to promote
the use of Unfired Earth as a building medium
throughout Australia.”
The materials for making mud bricks are
readily available in most areas and may be
sourced directly from the site of the building in
some cases.
Low costs in construction can only be
effectively achieved by self-build, reducing the
labour costs associated with manufacture and/
or laying of bricks. Commercially produced mud
brick construction can be as expensive, or even
more expensive, than brick veneer.

Construction process
Mud brick wall construction has generally
been the province of owner-builders, but a
large proportion of mudbrick buildings are now
constructed by or with the help of commercial
builders. The potential for sourcing the main
wall construction material from one’s own site,
making the bricks, and building the walls, can
be very appealing as both an economic and
lifestyle choice. As a result, the first stage of
construction may involve excavating the mud
from the site.

Paul Downton

Introduction]

Buildability, availability and cost
Mud bricks provide a forgiving construction
medium well suited to owner-builder
construction. There are a number of
proprietary mud brick makers and builders
able to provide good information and a strong
owner-builder oriented network. There are

The clay content of adobe can range
between 30 and 70 per cent and the overall
earth content may also include silt, gravel
and stones. There are a number of tests
for suitability of the earth and the approval
process may require an erosion test. Before
excavating for on-site mud, consider the site
layout to minimise carrying and transport and
ensure there is space to keep any topsoil
separate for use on the garden.
Owner builders should recognise that mud
brick making is a labour intensive activity.
A house may require around 10,000 bricks,
but a working couple would be lucky to
average a production rate of 200 a week.
Mud brick moulds can be made from wood

A typical standard mud brick is between
300-375mm long, 250-300mm wide and
125mm high and can weigh up to 18kg – as
much as a straw bale! Smaller brick sizes
are recommended for owner building. Mud
bricks can be made in a range of sizes and
moulds and can be made in special shapes
for fitting around structural elements and
accommodating pipes and wires. Stabilised
mud bricks may contain materials such as
straw, cement or bitumen. [See: 5.8 Straw
Bale]

TYPICAL DOMESTIC
CONSTRUCTION

In a similar way, the greenhouse gas emissions
associated with unfired mud bricks can (and
should) be very low. To keep emissions to
an absolute minimum, the consumption of
fossil fuel and other combustion processes
have to be avoided. [See: 5.1 Material Use

or metal. Bricks must dry evenly to avoid
cracking and they should be covered to
avoid direct sunlight and overly quick drying
out. There are a number of mud brick
manufacturers that cater to the market for
people who do not have the time or resources
to make their own.

Although adobe can be load bearing, there
is also widespread use of frames. The
advantages of this are that a roof structure
can be erected to provide weather protection
for both mud brick making and construction.
Disadvantages include the need to connect
with and build around frame structures.
After the footings have been placed and
the bricks are ready for laying, the building
process is similar to that of any other masonry
construction.
All structural design should be prepared
by a competent person and may require
preparation or checking by a qualified
engineer. Qualified professionals, architects
and designers provide years of experience
and access to intellectual property that has
the potential to save house builders time and
money as well as help ensure environmental
performance. All masonry construction has to
comply with the Building Code and Australian
Standards. For example, all masonry walls are
required to have movement/expansion joints
at specified intervals.

Footings
It is possible to make footings from rubble,
but unconventional construction may make
it harder to obtain building approvals and
the usual method is to employ strip or raft
concrete footings. A raft concrete slab can
provide a clean, flat surface for making mud
bricks. A damp proof course must be laid
between the footings and brick wall to
prevent rising damp. A ‘splash course’ of
fired bricks is advisable to prevent erosion
of the lower course of mud bricks resulting
from heavy rain.

5.6 MUD BRICK (Adobe)

Frames

The mud Mortar bed are normally quite thick
and needs to provide complete bedding for the
bricks. Perpends are similarly thick (about 20 –
30mm). The intention is to produce a wall that
is effectively monolithic, ie. as if it were a single
piece of material.

Mud bricks can be load bearing but it is also
usual Australian practice to build mud brick
walls between timber or steel frames.

Load bearing walls
Load bearing mud brick wall construction
requires particular attention to good bonding
(avoiding continuous vertical joints) and
ensuring stability by having returns on the walls
that buttress them against sideways forces.
Again, normal, traditional masonry practice
applies to the pattern in which bricks should be
laid. It is possible to create arches, squinches
and domes in mud brick and although these
have featured in adobe structure since time
immemorial, they are rare in modern building
structures of this type.

Joints and connections
Mud bricks are laid on thick mortar beds that
are essentially the same mix as the brick, but
in its ‘muddy’ state. It is also common practice
in the commercial mudbrick industry to use
a sand-cement mortar. Once dried, it can be
difficult to distinguish between mortar bed and
brick and some adobe aesthetics exploit this
‘seamless’ appearance to create a monolithic
effect. The roof timbers or steel members can
spring from the columns (particularly in the case
of steel) or bear on wallplates. It is generally
recommended that roofs have considerable
overhang in order to provide some protection to
walls from driving rain. In more sheltered areas
this requirement is less vital, but care must be
taken to provide a good quality render and
waterproofing finish, see ‘Finishes’.

Fixings
Fixings to mud brick need to allow for the
relatively poor ‘pull-out’ strength of the material.
Strong fixings can be achieved by embedding
dowels or plugs into a wall – the depth and type
of which should be determined by reference to
a skilled builder or engineer if the load carrying
capacity of the fixing is critical.

Openings
Lintels can be in any structurally appropriate
material, although timber is typically used.
Beams and lintels can be formed from quite
‘rough and ready’ timber and readily blended
into the mud brick construction. Mud bricks
can be also be laid to form arches, particularly
over small spans (less than a metre), and even
domes, although this requires high levels of
bricklaying skills as well as more stringent
demands from engineering and approvals
processes.

Finishes
Linseed oil and turpentine can be used to
provide a final finish. This is also a very effective
method of protecting walls susceptible to
erosion. There is even the option of using
the natural plastic of cellulose, processed by
bovine beasts, to create mud and manure
slurry, although this is seldom used in Australia.
Finishes can range from rustic to smooth with
this typical flexibility of approach being one of
the material’s many appealing qualities.

After brushing to get a fairly even surface, the
final finish is a mud slurry, typically finished
by hand. This slurry may also be the final
waterproofing coat (eg. A mud and cow dung
mix) or it may have a further clear coat of
proprietary waterproofing material. Linseed
oil and turpentine can be used to provide a
final finish.